The present invention relates to a method an apparatus for the recovery of heat from a steam boiler, and more particularly to a unit which is useful in connection with a steam boiler to recover thermal energy from the flash steam water and from sensible heat left in the boiler water.
Boilers are used to generate steam by boiling water. The water within the boiler which remains after steam has been generated will be subject to the concentrating effect of minerals and other contaminants in the water which will not pass into the steam phase. If over concentration of dissolved impurities occurs, scale forms and thermal efficiency is lost. To prevent over concentration in steam generation processes, water must be periodically removed from the steam boiler. The process of removing dissolved impurities is called blowdown. A volume of concentrated boiler water is removed and then subsequently replaced by higher purity boiler feedwater which naturally is cooler than the water which was in the boiler. This process occurs throughout the operation cycle of the boiler.
Boilers produce steam under pressure. The higher the pressure, the greater the temperature. In the prior art, when the blowdown process is executed, the hot boiler water at operating pressure is piped to a blowdown tank. The change in pressure between operating pressure and atmospheric pressure, results in the formation of a steam plume. The size of this plume is dependent upon the operating pressure and temperature. The higher the pressure, the greater the plume that is generated.
In most applications, such as the one disclosed in the U.S. Pat. No. 4,428,328, to Ratliff, this plume is released in a vessel called a flash tank or a blowdown tank. Flash tanks, except for very high-pressure applications are generally open to atmosphere. Thus, the flash steam and the heat contained therein is lost to the surrounding atmosphere. As that happens, the heat energy reserved in the flash steam is wasted.
Once the flash steam has been released, it is the practice in the prior art to send the remaining mass of blowdown water to sewer, via a heat exchanger, where energy is transferred from the blowdown water to the feedwater which is being added to the boiler.
Other devices and apparatus have been proposed which benefit from the thermal energy contained in the flash steam at the expense of wasting the energy contained in the blowdown water.
To overcome the limitations of the prior art described above, and to overcome other limitations that will become apparent upon reading and understanding the present specification, the present invention provides a cost effective method and simplified means for combining the two fundamental elements which prevent the loss of energy during the necessary process of blowing down steam boilers to prevent scale formation. The present invention recovers the heat from both the blowdown water and the flash steam.